1. Field of the Invention
The present invention relates to an epoxy resin composition for a prepreg used for manufacturing a printed-wiring board or a multilayer printed-wiring board, a prepreg, and a multilayer printed-wiring board.
2. Description of the Background Art
A nonflammable epoxy resin is used in a variety of electrical insulating materials due to the excellent self-extinguishing property, mechanical property, water-vapor resistance and electrical property.
The previous nonflammable epoxy resins contain a halogen system compound including mainly bromine in order to impart nonflammability and this affords the self-extinguishing property to molded particles. However, when such the molded articles burn upon firing or the like, there is a possibility that compounds harmful to the human body such as polybrominated dibenzodioxin, furan and the like are formed. Moreover, when compounds containing bromine are heated, bromine is released by decomposition and, thus, the heat resistance in long term is deteriorated. For that reason, there is desired development of molded articles having the excellent nonflammability and heat resistance without adding a halogen system compound.
As a strategy to this problem, flame-retardation using mainly a phosphorus element is being studied. For example, by incorporating an addition-type phosphorus system flame-retardant such as triphenyl phosphate (TPP), tricresyl phosphate (TCP), cresyldiphenyl phosphate (CDP) and the like which are a phosphate system compound into an epoxy resin composition, the nonflammability can be maintained. However, since general phosphorus compounds described above do not react with an epoxy resin, other problems arise that the solder heat resistance after moisture absorption and the resistance to chemicals such as the alkali resistance and the like of molded articles are significantly reduced.
Then, as disclosed in JP-A 4-11662, JP-A 11-166035 and JP-A 11-124489, the use of phosphorus compounds having the reactivity with an epoxy resin is proposed. However, even when these phosphorus compounds are used, the properties such as the solder heat resistance after moisture absorption and the like are not sufficient as compared with previous nonflammable epoxy resins using a halogen system compound. In addition, even when widely used general resins such as bisphenol A-type epoxy resin are used, a glass transition temperature (hereinafter, referred to as Tg) of a molded article is lowered and, furthermore, in the case of a printed-wiring board and a multilayer printed-wiring board using this molded article, the adhering force between layers of a laminated sheet or to a copper foil of an inner layer substrate is reduced.
One reason why more excellent solder heat resistance over the previous one is required in addition to nonflammability is a problem of today""s earth environment. That is, release of lead used in a solder material into the natural environment has become a serious problem and, as one strategy thereto, the use of a lead-free solder has been initiated. Pursuant to this, a solder treating temperature is elevated higher by about 10 to 15xc2x0 C. than the previous temperature and, thus, there arises a difficulty that the aforementioned techniques can not deal therewith.
The present invention was done in view of the above problems and an object thereof is to provide an epoxy resin composition for a prepreg used in manufacturing a printed-wiring board and a multilayer printed-wiring board which do not produce harmful substances upon burning, are excellent in the nonflammability, the solder heat resistance after moisture absorption and the adherability and has a high Tg at molding, a prepreg and a multilayer printed-wiring board.
An epoxy resin composition relating to the present invention is an epoxy resin composition comprising, as an essential component, a phosphorus compound having an average of not less than 1.8 and less than 3 of phenolic hydroxy groups reactive with an epoxy resin and an average of not less than 0.8 of a phosphorus element in the molecule, an inorganic filler having an average particle diameter of not greater than 30 xcexcm, a bifunctional epoxy resin having an average of not less than 1.8 and less than 2.6 of epoxy groups in the molecule and a hardener, wherein the bifunctional epoxy resin is contained at an amount of not less than 51% by mass relative to the whole epoxy resin, dicyandiamide is used as the hardener and a ratio (a/c) of equivalent (a) of a phenolic hydroxy group of the phosphorus compound and equivalent (c) of an epoxy group of the bifunctional epoxy resin is not less than 0.3 and less than 0.75, and an epoxy resin composition relating to the present invention is an epoxy resin composition comprising, as an essential component in the molecule, a phosphorus compound having an average of not less than 1.8 and not less 3 of phenolic hydroxy groups reactive with an epoxy resin and an average of not less than 0.8 of a phosphorus element, an inorganic filler having an average particle diameter of not greater than 30 xcexcm, a bifunctional epoxy resin having an average of not less than 1.8 and less than 2.6 of epoxy groups in the molecule and a hardener, wherein the bifunctional epoxy resin is contained at an amount of not less than 51% by mass relative to the whole epoxy resin, a polyfunctional phenol system compound having an average of not less than 3 phenolic hydroxy groups in the molecule is used as the hardener and a ratio (a/c) of equivalent (a) of a phenolic hydroxy group of the phosphorus compound and equivalent (c) of an epoxy group of the bifunctional epoxy resin is not less than 0.3 and less than 0.75.
Embodiments of the present invention will be explained below.
A phosphorus compound in the present invention is not particularly limited as long as it has an average of not less than 1.8 and less than 3 of phenolic hydroxy groups reactive with an epoxy resin and an average of not less than 0.8 of a phosphorus element in the molecule. When such the phosphorus compound having a bifunctional phenolic hydroxy group and a bifunctional epoxy resin described below are reacted, a linear polymer compound can be obtained. And, when this compound is cured with a hardener described below, a molded article having the excellent toughness, flexibility, adherability and stress relaxation upon heating can be obtained. Here, when the number of phenolic hydroxy groups is an average of less than 1.8, it becomes difficult to react with a bifunctional epoxy resin to produce the aforementioned linear polymer compound. On the other hand, when the number of phenolic hydroxy groups is an average of not less than 3, a product by a reaction with a bifunctional epoxy resin is gelatinized and, thus, it becomes difficult to stably manufacture an epoxy resin composition. In addition, when the number of a phosphorus element is less than 0.8, it becomes difficult to impart the sufficient nonflammability.
As an example of a phosphorus compound, phosphorus compounds having a bifunctional phenolic hydroxy group represented by the formula (1) to (3) are preferable and these are particularly excellent in the nonflammability, the heat resistance and the like.
Here, a ratio (a/c) of equivalent (a) of a phenolic hydroxy group of a phosphorus compound and equivalent (c) of an epoxy group of a bifunctional epoxy resin is set at not less than 0.3 and less than 0.75. By setting like this, the aforementioned linear polymer compound can be sufficiently produced and, as a result, a molded article having the excellent toughness, flexibility, adherability and stress relaxation upon heating can be obtained. To the contrary, when this ratio is less than 0.3, such properties can not be obtained. When the ratio is not less than 0.75, Tg tends to be lowered.
Furthermore, it is preferable to set the content of a phosphorus element component at not less than 0.8% by mass and less than 3.5% by mass of the whole resin solids constituent in an epoxy resin composition and, by setting like this, the sufficient nonflammability can be maintained without adding a halogen compound. To the contrary, when the content is less than 0.8% by mass, there is a possibility that it becomes difficult to obtain the sufficient nonflammability. When the content is not less than 3.5% by mass, there is a possibility that increase in moisture absorption and decrease in the heat resistance tend to occur.
Next, an inorganic filler is not particularly limited as long as it has an average particle diameter of not greater than 30 xcexcm. By adding such the inorganic filler to an epoxy resin composition, water absorption can be reduced, the strength upon heating at an elevated temperature such as solder treatment or the like can be increased, and a dimensional change rate upon heating can be reduced. Further, such the fine inorganic filler can improve the transparency of a molded article and, for this purpose, when an inorganic filler having an average particle diameter of not greater than 5 xcexcm is used, the better effects can be expected. To the contrary, when an average particle diameter exceeds 30 xcexcm, the transparency of a molded article is reduced, the electrical insulating properties are reduced and, further, the stress relaxation effect becomes uniform and, thus, the solder heat resistance after moisture absorption is reduced. In addition, a lower limit of an average particle diameter is 0.05 xcexcm and, when the diameter is less than 0.05 xcexcm, there is a possibility that the viscosity of an epoxy resin composition is increased.
As an example of an inorganic filler, metal hydroxides such as aluminum hydroxide, magnesium hydroxide and the like are preferable and these can make a contribution to the nonflammability in addition to the aforementioned effects.
Here, it is preferable to set an amount of the inorganic filler to be added at not less than 15 parts by mass and less than 100 parts by mass relative to 100 parts by mass of resin solids constituents and, by setting like this, water absorption can be reduced, the strength upon heating at an elevated temperature such as solder treatment and the like can be increased, and dimensional change rate upon heating can be reduced. In addition, it is preferable to add an amount of not less than 35 parts by mass. To the contrary, when an amount to be added is less than 15 parts by mass, there is a possibility that water absorption is increased, the solder heat resistance is reduced, and dimensional change rate upon heating is increased. When the amount is not less than 100 parts by mass, it is difficult to disperse a filler uniformly and there is a possibility that the adhering force is reduced.
Further, it is preferable that the surface of an inorganic filler to be added to an epoxy resin composition is treated with an epoxysilane coupling agent or a mercaptosilane coupling agent. When an inorganic filler is subjected to the surface treatment like this, the adhering force to a resin can be strengthened and, further, the properties of an inorganic filler itself can be improved. That is, although aluminum hydroxide and magnesium hydroxide do not have sufficient resistance to chemicals, they can improve resistance to chemicals by the surface treatment. When an epoxysilane coupling agent or a mercaptosilane coupling agent is used for this surface treatment, the properties such as resistance to chemicals and the like can be improved and, at the same time, an inorganic filler can be dispersed uniformly in an epoxy resin composition while inhibiting secondary aggregation of the inorganic filler. Here, as an example of the epoxysilane coupling agent, there are xcex3-glycidoxypropyltrimethoxysilane and xcex3-glycidoxypropylmethyldimethoxysilane. As an example of the mercaptosilane coupling agent, there are xcex3-mercaptopropyltrimethoxysilane and xcex3-mercaptopropyltriethoxysilane.
In addition, an epoxy resin is not particularly limited as long as it is a bifunctional epoxy resin having an average of not less than 1.8 and less than 2.6 of epoxy groups in the molecule. When the number of epoxy groups is an average of less than 1.8, it becomes difficult to react with the aforementioned phosphorus compound to produce a linear polymer compound. On the other hand, the number is an average of not less than 2.6, it becomes difficult to stably produce an epoxy resin composition because a reaction product with a phosphorus compound is gelatinized.
As an example of an epoxy resin, bifunctional epoxy resins represented by the formulas (4) to (7) are preferable. When these are used, Tg of a molded article can be heightened and, at the same time, the strength upon heating at an elevated temperature becomes better due to stiffness. Therefore, when a printed-wiring board or a multilayer printed-wiring board using epoxy resin composition having such properties is manufactured, the adhering force to a metal foil such as a copper foil is not reduced and the electrical conductivity reliance of a through-hole can be sufficiently maintained in spite of a temperature change after processing of a through-hole.
In addition, among examples of the aforementioned epoxy resin, since bifunctional epoxy resins represented by the formulas (4) to (6) have a high carbon rate in a resin skeleton, name retardation of these bifunctional epoxy resins can be particularly easily attained by the addition of a phosphorus compound.
Here, a bifunctional epoxy resin is contained at an amount of not less than 51% by mass relative to the whole epoxy resin and this can improve toughness and the like. To the contrary, when the content is less than 51% by mass, the adhering force is reduced and the solder heat resistance is reduced.
In addition, as a hardener, dicyandiamide or a polyfunctional phenol system compound having an average of not less than 3 of phenolic hydroxy groups in the molecule is used. These can impart the better electrical properties and, at the same time, harden a linear polymer compound which is a reaction product of the aforementioned phosphorus compound having a bifunctional phenolic hydroxy group and a bifunctional epoxy resin and, thus, a molded article having the excellent toughness, flexibility, adherability and stress relaxation upon heating can be obtained. In addition, when a polyfunctional phenol compound has an average of less than 3 of phenolic hydroxy groups, it becomes a hardened compound having low Tg.
Other epoxy resins, additives and various modifiers may be incorporated into an epoxy resin composition in addition to the aforementioned essential components, as necessary.
For example, as other epoxy resins, bifunctional epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin and the like, and polyfunctional epoxy resins such as phenol novolak-type epoxy resin, cresol novolak-type epoxy resin, bisphenol A novolak-type epoxy resin, bisphenol F novolak-type epoxy resin, naphthalene-type epoxy resin, biphenyl-type epoxy resin, dicyclopentadiene-type epoxy resin and the like can be used alone or in combination of a plurality of them. Provided that, general-purpose novolak-type epoxy resin hardens a molded article after curing and is inferior in toughness and the like and, when a polyfunctional epoxy resin is used together, it is desirable to use a polyfunctional epoxy resin with toughness imparted thereto.
In addition, as a hardening promotor, tertiary amines and imidazoles may be added.
In addition, as a reforming agent, a rubber component such as polyvinylacetal resin, SBR, BR, butyl rubber, butadiene-acrylonitrile copolymer rubber and the like may be incorporated.
And, an epoxy resin composition relating to the present invention can be manufactured by two processes described below.
According to the first manufacturing process, the aforementioned phosphorus compound, inorganic filler, epoxy resin and hardener as an essential component and, if necessary, other components can be mixed uniformly with a mixer, a blender or the like to manufacture an epoxy resin composition.
According to the second manufacturing process, first, all or a part of a bifunctional epoxy resin and all of a phosphorus compound having a bifunctional phenolic hydroxy group are heated and reacted using tertiary amines or triphenylphosphines. Upon this, not less than 80%, more preferably not less than 95% of phenolic hydroxy groups of a phosphorus compound are reacted with an epoxy group of a bifunctional epoxy resin. The resin thus produced is referred to as xe2x80x9cpre-reacted epoxy resinxe2x80x9d.
Next, an inorganic filler, a hardener and, if necessary, a phosphorus compound, an epoxy resin and other components are incorporated into this pre-reacted epoxy resin, which can be uniformly mixed with a mixer, a blender or the like to manufacture an epoxy resin composition.
In addition, in any aforementioned manufacturing processes, a solvent may be or may not be used.
Here, an epoxy resin composition relating to the present invention is preferably manufactured according to the second manufacturing process as compared with the first manufacturing process. This is based on the following reasons. That is, when the aforementioned phosphorus compound having a bifunctional phenolic hydroxy group and the bifunctional epoxy resin are not reacted, it is likely to reduce the solder heat resistance after moisture absorption and the resistance to chemicals. For this reason, it is necessary to sufficiently react both of them. However, in the first manufacturing process, it is difficult to react only these two component because other components are present in some cases. Then, by reacting only these two component in advance, a linear polymer compound is assuredly produced. In addition, both of them have a bifunctional group, a prereacted epoxy resin can be stably manufactured without gelation.
And, a prepreg in the semi-hardened state (B-stage) can be manufactured by preparing a varnish using the epoxy resin composition prepared by the aforementioned manufacturing process, impregnating a substrate with the varnish, and drying the substrate at 120 to 190xc2x0 C. for 3 to 15 minutes in a dryer. As a substrate, a glass fiber cloth such as a glass cloth, a glass paper, a glass mat and the like, a kraft paper, a linter paper, a natural fiber cloth, an organic synthetic fiber cloth and the like can be used.
A laminated sheet can be manufactured by stacking a required number of prepregs thus manufactured and heating and pressing them under the conditions of 140 to 200xc2x0 C. and 0.98 to 4.9 MPa. Upon this, a metal foil-clad laminated sheet can be manufactured by overlaying a metal foil on one side or both sides of a stack of a required number of prepregs and heating and pressing the prepregs and the metal foil. As this metal foil, a copper foil, a silver foil, an aluminum foil, a stainless foil and the like can be used. In addition, a multilayer laminated sheet can be manufactured by placing a prepreg on an upper side and a lower side of an inner layer substrate on which a circuit pattern is pre-formed, overlaying a metal foil on one side or both sides of a stack of a required number of prepregs, and heating and pressing the prepregs and the metal foil. In addition, upon manufacturing a multilayer laminated sheet, it is preferable to set a molding temperature in a range of 150 to 180xc2x0 C.
When a molding temperature is lower than 1 50xc2x0 C., there is a possibility that hardening is insufficient, it becomes difficult to obtain the desired heat resistance, and the adhering force between a prepreg and a copper foil of an inner layer substrate becomes insufficient. When the temperature is higher than 180xc2x0 C., the irregular surface of a copper foil of an inner layer substrate which has been chemically treated in advance is disappeared, and there is a possibility that the adhering force between a prepreg and a copper foil of an inner layer substrate becomes insufficient.